1. Field of the Invention
The present invention relates to a radar device, which employs a transmission changeover digital beam forming (DBF) system to measure an object.
2. Description of the Related Art
As a technique that receives electric waves that arrive from an external by means of a plurality of receiving elements, and combines the electric waves that have been received by the respective receiving elements through signal processing to discriminate the signals in each of arrival directions, there is known a technique that is called “digital beam forming”.
As a technique for improving angular resolution when applying the DBF technique to a radar antenna, there has been proposed to change over the plurality of transmitting elements in time division to be used, thereby increasing an equivalent aperture with an array antenna having a small number of elements to narrow a beam width (for example, refer to JP 2004-198312 A).
However, in the radar disclosed in JP 2004-198312 A, when virtual receiving elements are arranged at irregular intervals, fast Fourier transform cannot be used as Fourier transform for conducting beam forming. The Fourier transform can be executed by an application of the general discrete Fourier transform, but the operation amount is remarkably increased as compared with the case of applying the fast Fourier transform. This is because, when it is assumed that a signal length is N, the operation amount of the fast Fourier transform is proportional to N log N, whereas the operation amount of the Fourier transform that is not made fast is proportional to N2.